As the use of horizontal and directional drilling has grown, and more sensors and actuators are integrated into the drilling assemblies, the need for power in the borehole has also grown. Various types of equipment, from surveying to bit positioning, formation evaluation to fluid control all require some form of power. Numerous methods of transmitting power from the surface to devices within the borehole have been used, including placing cables in an annulus formed between the borehole and casing and using electrical conduction through the casing. Batteries have also been used. However the use of batteries within boreholes presents problems with respect to space and battery life, which can become particularly acute in high temperature boreholes. Various types of downhole power generation have been used. However, these methods often involve equipment that may be unwieldy, due to either length or circumference, or are underpowered for the power demand.
What is needed is a downhole power generation method and apparatus with an extended life time for generating electricity that is self-contained and can be proportioned for various boreholes.